1. Field of the Invention
The present invention relates to a magnetic resonance imaging system and a magnetic resonance imaging method for dynamically imaging using a technique of making a data acquisition frequency for some areas in k space different from that of other areas.
2. Description of the Related Art
A technique of further enhancing the data acquisition frequency for an area closer to the center of k space is known as a technique for improving the effective temporal resolution in contrast MRA (Magnetic Resonance Angiography). This technique is called, for example, TRICKS (Time Resolved Imaging of Contrast Kinetics) or DRKS (Different Rate k-space Sampling). Hereinafter, this technique is referred to as “DRKS”.
In DRKS, k space is divided into plural acquisition areas from the center thereof to the outer edge. The data acquisition frequency is more enhanced in the acquisition area closer to the center of the k space. In DRKS, since data on the central area of k space, that is, the low-frequency components of a magnetic resonance signal, can be acquired with a relatively higher frequency, it is possible to dynamically image with higher contrast and higher temporal resolution. In general, the plural acquisition areas are set so that the amounts of acquired data in the acquisition areas are equal to each other. The number of acquisition areas is determined depending on the desired speed-up rate. For example, 1.5 times, 2 times, 3 times and the like are realized as the speed-up rate and the numbers of acquisition areas corresponding to the speed-up rates are 3, 4, 6, and the like, respectively.
DRKS is disclosed in JP-A-2004-24783 (U.S. Pat. No. 6,914,429).
However, in contrast MRA employing DRKS, an image in which a contrast agent flows in a relatively thick blood vessel is drawn out with high contrast. Since the data acquisition frequency for intermediate-frequency to high-frequency components is relatively smaller, it is difficult to image fine blood vessels with high precision.